99mTc-maraciclatide is the recommended INN (USA Approved Name) for 99mTc-NC100692. 99mTc-NC100692 has been described in both patents and publications, as a radiopharmaceutical which targets integrin receptors in vivo.
WO 03/006491 discloses compounds of Formula (I):
or pharmaceutically acceptable salt thereofwherein:                G represents glycine        D represents aspartic acid        R1 represents —(CH2)n— or —(CH2)n—C6H4— wherein        n represents a positive integer 1 to 10,        h represents a positive integer 1 or 2,        X1 represents an amino acid residue wherein said amino acid possesses a functional side-chain such as an acid or amine,        X2 and X4 represent independently an amino acid residue capable of forming a disulfide bond,        X3 represents arginine, N-methylarginine or an arginine mimetic,        X5 represents a hydrophobic amino acid or derivatives thereof,        X6 represents a thiol-containing amino acid residue,        X7 is absent or represents a biomodifier moiety,        Z1 represents an anti-neoplastic agent, a chelating agent or a reporter moiety and        W1 is absent or represents a spacer moiety.        
WO 03/006491 discloses that a preferred chelating moiety has the formula shown, and includes 99mTc complexes of said chelator conjugate of Formula I therein:

WO 03/006491 does not disclose kits.
Edwards et al [Nucl. Med. Biol., 35, 365-375 (2008)] disclose that 99mTc-maraciclatide (99mTc-NC100692) can be prepared from a kit. Edwards et al state that each lyophilised kit contains approximately 44 nmol maraciclatide (NC100692), plus a number of excipients including buffer, stannous reducing agent and methylene diphosphonic acid (present as a Sn2+ solubiliser). Edwards et al report that the radiochemical purity (RCP) of each reconstituted kit was determined at 20 minutes post reconstitution, and was found to be at least 90%. The RCP was found to be stable over the period that the reconstituted kits were used.
The Present Invention.
Technetium-99m (99mTc) is a radioisotope which decays with a half-life of 6.02 hours to technetium-99 (99Tc). The radioactive decay is accompanied by the emission of a gamma ray with an energy that is near ideal for medical imaging with a modern gamma-camera. The decay product, 99Tc, is also radioactive and decays by β-emission with a half-life of 2.1×105 years (to the stable isotope 99Ru), but the radioactive emissions from 99Tc are insufficient for medical imaging.
Conventional 99mTc “generators” comprise the radioisotope 99Mo, which decays with a half-life of 66.2 hours. The chemical form of the technetium eluted from such a generator is 99mTc-pertechnetate. About 86% of 99Mo decays result in the production of 99mTc, however ca. 14% of 99Mo decays result in the direct production of 99Tc. Therefore, if a 99mTc generator is eluted a very short time after the previous elution, the 99mTc content will be low but will be about 86% of the total technetium content. As time passes since the previous elution of the generator, 99Tc is being produced both from 99Mo and from the decay of 99mTc to 99Tc. Consequently, as the time interval between generator elutions increases, the 99Tc/99mTc ratio increases. The 99Tc and 99mTc technetium isotopes are chemically identical, and consequently any radiopharmaceutical preparation must be able to cope with a wide range of 99Tc chemical content in the eluate in order to be able to function effectively over the usable lifetime of the generator. It is also the case that elutions made with a fresh 99mTc generator are likely to have a higher radioactive concentration, and thus have a higher concentration of reactive free radicals arising from radiolysis of the solvent (water). A viable 99mTc radiopharmaceutical preparation thus needs to be able to provide satisfactory RCP performance even when such reactive free radicals are present. These characteristics of the 99mTc generator are illustrated in most radiochemistry or nuclear chemistry textbooks, and the problems that different eluate properties can give to the performance of 99mTc kits have been described by Saha, G. B. “Radiopharmaceuticals and Methods of Radiolabeling”; Chapter 6 (pages 80-108) in Fundamentals of Nuclear Pharmacy (3rd Edn.).
The present inventors have found that the Maraciclatide kit reported by Edwards et al (above) suffers from various problems not previously recognised in the prior art:                (i) relatively low initial RCP post-reconstitution of the kit with 99mTc-pertechnetate;        (ii) insufficient post-reconstitution stability;        (iii) the need to store and ship the kit at −15 to −20° C. to maintain kit stability and performance;        (iv) only a single patient dose being obtainable from the kit.        
The present invention provides improved 99mTc-maraciclatide radiopharmaceutical compositions which exhibit more reproducible initial radiochemical purity (RCP) and improved stability post-reconstitution, so that an RCP of 85 to 90% is maintained at 6 hours post-reconstitution. The problem of unsatisfactory RCP for 99mTc-maraciclatide preparations under certain conditions of radioactivity levels, radioactive concentrations or reconstitution volumes was not recognised in the prior art. Such conditions are those that could arise under normal conditions of use of a commercial radionuclide generator, such as a 99mTc generator.
Berger [Int. J. Appl. Rad. Isotop., 33, 1341-1344 (1982)] discloses that a wide range of antioxidants can be used to stabilise 99mTc-radiopharmaceuticals. Methylene Blue and ascorbic acid have since been highlighted as particularly suitable stabilisers [Weisner et al, Eur. J. Nucl. Med., 20, 661-666 (1993) and Liu et al, Bioconj. Chem., 14(4), 1052-1056 (2003)].
The present inventors have also established that the well-known radioprotectant ascorbic acid/ascorbate actually has a deleterious effect on the RCP of 99mTc-maraciclatide. A further known radioprotectant gentisic acid caused discolouration problems which negated its use in the present composition. The present invention provides compositions comprising a radioprotectant which solve this previously unrecognised problem. The kits of the present invention have the advantages of: higher initial RCP; more robust RCP over longer time periods post-reconstitution; compatibility with various commercial 99mTc radiopharmaceutical generators and under a range of elution conditions; the facility to obtain two patient doses per kit (i.e. to reconstitute successfully with higher levels of radioactivity); adequate stability to be stored and shipped at fridge (+5±3° C.) rather than freezer temperature (−10 to −20° C.) and kit shelf-life stability of at least 3 years.